Method for electrolytically fluorinating organic compounds

ABSTRACT

IN AN ELECTROFLUORINATION PROCESS HAVING FLUORINATABLE FEEDSTOCKS ELECTROCHEMICALLY FLUORINATED INN THE PORES OF THE POROUS ANODE OF AN ELECTROLYSIS CELL, THE FLUORINATABLE FEEDSTOCKS DELIVERED TO THE CELLARE PERIODICALLY REPLACED WITH A SECOND FLUID BEING ONE OF WATER VAPOR, NITROGEN OXIDE CARBON MONOXIDE OR HYDROGEN WHILE MAINTAING THE CELL UNDER ELECTROLYSIS CONDITIONS FOR CLEANING MATERIAL FROM THE ANODE OF THE CELL.

United States" Patent Oflice 3,806,432 Patented Apr. 23, 1974 3,806,432 METHOD FOR ELECTROLYTICALLY FLUORINAT- ING ORGANIC COMPOUNDS King L. Mills, Bartlesville, kla., assignor to Phillips Petroleum Company No Drawing. Filed July 27, 1972, Ser. No. 275,557

Int. Cl. C07b 29/06; C07c 17/10, 19/08 U.S. Cl. 204-59 F Claims ABSTRACT OF THE DISCLOSURE In an electrofluorination process having fluorinatable feedstocks electrochemically fluorinated in the pores of a porous anode of an electrolysis cell, the fluorinatable feedstocks delivered to the cell are periodically replaced with a second fluid being one of water vapor, nitrogen oxide, carbon monoxide, or hydrogen while maintaining the cell under electrolysis conditions for cleaning material from the anode of the cell.

It is desirable to provide a method for cleaning material from the anode of an electrolysis cell having fluorinatable feedstocks electrochemically fluorinated therein.

This invention therefore resides in an electrofluorination process having fluorinatable feedstocks electrochemically fluorinated in the pores of a porous anode of an electrolysis cell, in which the fluorinatable feedstocks delivered to the cell are periodically replaced with a second fluid being one of water vapor, nitrogen oxide, carbon monoxide, or hydrogen while maintaining the cell under electrolysis conditions for cleaning material from the anode of the cell. Hydrogen is preferred because it has the ability to regenerate the electrolyte by forming I-[F which will reestablish the desired HF:KF ratio in the crystallized electrolyte.

In an electrofluorination process, such as for example that process set forth in U.S. 3,511,760, a porous anode is immersed in an electrolyte. Fluorinatable feedstocks are brought into contact with the porous anode of an electrolysis cell where it is electrofluorinated to produce a valuable fluorinated hydrocarbon which is recovered therefrom. During the fluorination process, byproducts of the process such as for example salts, relatively high boiling intermediates between the organic feedstock and the fluorinated organic material, and other materials are often maintained in and about the pores of the anode which causes a decrease in the efliciency of the cell thereby resulting in waste. This buildup of material on the anode can progress to values which will cause the cell to be inoperative in that free fluorine is formed, the anode and products of the cell are chemically attacked, and an undesirable heavy polymer product is formed.

It has surprisingly been discovered that the anode of the cell can be easily cleaned of the undesirable deposits by periodically replacing the fluorinatable feedstocks delivered to the cell with a second fluid being one of nitrogen oxide, carbon monoxide, water vapor, or hydrogen while maintaining the cell under electrolysis conditions.

These materials, and others which can be utilized in the method of this invention, are more polar than the high boiling intermediate products on the anode and thereby will replace these undesirable materials and thereafter the second fluids will themselves be fluorinated. This will result in leaving a cleaned anode surface for subsequently fluorination cycles.

In the method of this invention, it is preferred that the second fluid be passed through the cell in contact with the anode at a rate in the range of about 5 to about 25 standard cubic feet per hour. Lower rates are undesirable because the concentration of fluid in the anode is too low to be eflective. Higher rates are undesirable because too much fluid would be wasted by by-passing and there is danger of bubble formation in salt electrolyte resulting in electrolyte spattering.

It is also preferred that the fluorinatable feedstocks be replaced by the second fluid after fluorinated feedstocks have been electrochemically fluorinatable in the cell for a period of time required to partially plug the anode causing feed bypassing usually 'a period in the range of about 72 to about 144 hours ormore.

It is also preferred that the second fluid be passed to the cell at a temperature in the range of about 190 F. to about 250 F. Lower temperatures are undesirable because the electrolyte freezes. Higher temperatures are undesirable because of possible loss of HF by entrainment, which will result in freezing of electrolyte.

The second fluids can also be diluted with an inert gas prior to injecting the second fluid into the cell. Examples of diluents which can be utilized are as follows: helium, nitrogen, neon.

The following is an example of the method of this invention.

EXAMPLE A fluorination cell 6%" OD x 4%" ID x 28" long had been operating on a propane feedstock at 800 amps, 8.0 v. at 220 F. and a feed rate of 0.75 lb./hr. for about 96 hrs. During the latter period of operation conversion had diminished due to the accumulation of heavy products and some salt electrolyte deposition in the anode pores.

Feed was discontinued and hydrogen was introduced at an initial rate of 10.3 s.c.f./hr. while the cell operated at 11 amps and 5.5 volts at 200 F.

Initially 30% of the hydrogen feed bypassed the anode. After about minutes this had dropped to 11%, showing better flow through the anode pores. After 3 hours only 5% of the hydrogen feed bypassed the cell. The flow of hydrogen was then increased to 13.9 s.c.f./hr., after which time about 10% of the hydrogen bypassed the anode. After 7 hours, the feed was switched back to the original hydrocarbon for production of fluorinated product and the unit was gradually (over period of several hours) brought to full power. The cell was completely regenerated and operated successfully for 5 days when the unit was shut down. Y

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and example and it should be understood that this invention is not to be unduly limited thereto.

What is claimed is:

1. In an electrofluorination process having fluorinatable feedstocks electrochemically fluorinated in the pores of a porous anode of an electrolysis cell, the improvement comprising: after said porous anode has become partially plugged replacing the fluorinatable feedstocks delivered to the cell with a second fluid being one of water vapor, nitrogen oxide, carbon monoxide, or hydrogen while maintaining the cell under electrolysis conditions said feedstocks being replaced by the second fluid for a time suflicient for cleaning material from the anode of the cell.

2. A method, as set forth in claim 1, wherein the second fluid is passed through the cell in contact with the anode at a rate-in the range of about 5 to about 25 standard cubic feet per hour.

3. A method, as set forth in claim 1, including passing the second fluid into the cell at a temperature in the range of about to about 250 F.

4. A method, as set forth in claim 1, wherein the second fluid is dilutedwith an inert gas prior to injecting said fluid into the cell.

5. In an electrofluorination process having fluorinatable feedstocks electrochemically fluorinated in the pores of comprising: after said porous anode has become partially a porous anode of an electrolysis cell, the improvement plugged 1 replacing the fluorinatable feedstocks delivered to the cell with a second fluid being one of water vapor, nitrogen oxide, carbon monoxide, or hydrogen while maintaining the cell under electrolysis conditions, said feedstocks being replaced by the second fluid for a time suflicient for cleaning material from the anode of the cell and said second fluid being passed into the cell at a temperature in the range of about 190 to about 250 F. at a rate in the range of about 5 to about 25 standard cubic feet per hour.

References Cited UNITED STATES PATENTS 5/1972 Mills 204-59 R 10 FREDERICK C. EDM UNDSON, Primary Examiner 

